Convert frontend code to typescript (#31559)

None of the frontend js/ts files was touched besides these two commands
(edit: no longer true, I touched one file in
61105d0618
because of a deprecation that was not showing before the rename).

`tsc` currently reports 778 errors, so I have disabled it in CI as
planned.

Everything appears to work fine.

web_src/js/features/comp/WebHookEditor.ts

@@ -0,0 +1,44 @@
+import {POST} from '../../modules/fetch.ts';
+import {hideElem, showElem, toggleElem} from '../../utils/dom.ts';
+
+export function initCompWebHookEditor() {
+  if (!document.querySelectorAll('.new.webhook').length) {
+    return;
+  }
+
+  for (const input of document.querySelectorAll('.events.checkbox input')) {
+    input.addEventListener('change', function () {
+      if (this.checked) {
+        showElem('.events.fields');
+      }
+    });
+  }
+
+  for (const input of document.querySelectorAll('.non-events.checkbox input')) {
+    input.addEventListener('change', function () {
+      if (this.checked) {
+        hideElem('.events.fields');
+      }
+    });
+  }
+
+  // some webhooks (like Gitea) allow to set the request method (GET/POST), and it would toggle the "Content Type" field
+  const httpMethodInput = document.querySelector('#http_method');
+  if (httpMethodInput) {
+    const updateContentType = function () {
+      const visible = httpMethodInput.value === 'POST';
+      toggleElem(document.querySelector('#content_type').closest('.field'), visible);
+    };
+    updateContentType();
+    httpMethodInput.addEventListener('change', updateContentType);
+  }
+
+  // Test delivery
+  document.querySelector('#test-delivery')?.addEventListener('click', async function () {
+    this.classList.add('is-loading', 'disabled');
+    await POST(this.getAttribute('data-link'));
+    setTimeout(() => {
+      window.location.href = this.getAttribute('data-redirect');
+    }, 5000);
+  });
+}